This invention relates to magnetic recording media, and more particularly, to an improvement in the topcoat on magnetic recording media having a magnetic layer in the form of a continuous thin film.
Among magnetic recording media for use in video, audio and other applications, active research and development works have been mede on magnetic recording media, usually magnetic tapes having a magnetic layer in the form of a continuous thin film because of the compactness of a roll of tape.
The preferred magnetic layers for such continuous film type media are deposited films of Co, Co--Ni, Co--0, Co--Ni--O and similar systems formed by the so-called oblique incidence evaporation process in which cobalt and optional elements are evaporated in vacuum and directed at a given angle with respect to the normal to the substrate because such evaporated films exhibit superior characteristics. The deposited magnetic layers, however, have many disadvantages including high dynamic friction, low film strength, rough head contact, and low runnability (that is, the durability of tape which travels in frictional contact with rigid members in a video machine), resulting in reduced output after repeated travels. In the case of video application, the deposited magnetic layers exhibit a short life time when operated in the still mode (to be simply referred to as "still life", hereinafter). In addition, there occur many dropouts such layers.
Under these circumstances, a variety of topcoats have heretofore been proposed which cover obliquely evaporated magnetic layers. For example, Japanese Patent Application Kokai Nos. 53-88704 and 55-93533 disclose such topcoats formed from straight chain saturated fatty acids and esters thereof by eveporation and coating techniques. These prior art topcoats, however, are yet insufficient with respect to some of the above requirements, for example, runnability, still life, and dropout.